1. Field of the Invention
This invention is related to an adjusting method for a synchronous (sync) signal in an optical storage device, and more particularly is relating to an adjusting method for a sync signal in an optical storage device, used for searching for the synchronous impulses between windows.
2. Description of Related Art
In the recent years, related technologies for the optical industry is continuously developed. Taking the re-writable CD (CD-R/RW) drive as an example, the recording speed is improved rapidly. Moreover, the rewriting speed has been improved to 10 speed (10×), 12×, or even higher. However in the practical case, if the ability for recording/rewriting the optical disc in higher speed is desired to have full performance, it still has a point in technology to overcome. That is the issue of buffer under run.
About the situation of buffer under run in simple speaking, it means that the speed of data flowing out from the buffer is larger than the speed of data flowing into the buffer. During recording/rewriting the optical disc, data transferred from a host machine (for example, a personal computer) is stored into a buffer in the re-writable CD drive. The pick-up head of the re-writable CD drive will then record data onto the optical disc according to data stored in the buffer. Since the data transmitting speed from the computer is not constant, data stored in the buffer maybe be almost full in sometime and almost empty in other time. If the data transmitting speed from the computer is not sufficiently fast, the amount of data stored in the buffer decreases. When the amount of data stored in the buffer decreases under a threshold level, the re-writable CD drive will encounter a bad situation that there is no enough data for recording. This phenomenon is called the buffer under run. When the above situation occurs, recording data on to the optical disc is suddenly interrupted. This causes a failure of writing, and may cause a bad or defect disc.
If the computer executes other application programs during recording data on the re-writable CD, the data transmission speed from the computer to the rewritable CD drive may be negatively affected. As a result, the user often encounters the situation of buffer under run and even, a failure is occurred in recording CD. In general, a technology for preventing buffer under run, BURN-Proof or Just-Link, is proposed to avoid the above issue. This technology is briefly described as follows. When the amount of data stored in the buffer is reduced under to a threshold level, the re-writable CD drive will stop writing data onto the CD. At this time, the re-writable CD drive still continuously receives data transmitted from the computer and stores data into the buffer. When the buffer is accumulated enough, the re-writable CD drive is reactivated to record data on the disk at the location that the previous recording is terminated. From the above descriptions, it can be understood that via the BURN-proof or Just-Link technology, the probability about failure in recording disc is therefore reduced.
If the function of BURN-Proof technology is used during rewriting on the optical disc, a data gap between the previous recording location and the next recording location is generated. The length of this data gap is extremely small and related to the recording speed. For example, if the re-writable CD drive records data at 1× speed, then the data gap is about 40 microns. The data gap produced by the BURN-Proof technology will cause data on the optical disc to be discontinuous. This data gap will therefore also affect the synchronous signal with respect to data stored on the optical disc.
Referring to FIG. 1A that schematically illustrates the synchronous signal with respect to data stored on the optical disc without data gap. As shown in FIG. 1A, the synchronous signal 100 with respect to data on the optical disc without data gap is composed of a sequence of regular impulses. For example, the synchronous impulse 101 has a distance to the synchronous impulse 103 by an image frame, such as 588 T. In the same way, the synchronous impulse 103 has a distance to the synchronous impulse 105 by an image frame (588 T). Referring to FIG. 1B that schematically illustrates the synchronous signal with respect to data stored on the optical disc with a data gap. As shown in FIG. 1B, data between the synchronous impulse 111 and the synchronous impulse 113 is not interrupted by a data gap. Therefore, the distance between the two synchronous impulses 111 and 113 is equal to 588 T. However, a data gap exists between the two synchronous impulses 113 and 115 as shown in FIG. 1B. The data gap will cause the synchronous impulse 115, which is ideally expected to appear after the synchronous impulse 113 by 588 T, is then delayed. As a result, the distance between the synchronous impulse 113 and the synchronous impulse 115 is larger than 588 T. Then, since there is no data gap between the synchronous impulses 115 and 117, the distance between the synchronous impulses 115 and 117 is normal.
When the optical storage device, such as a CD-ROM drive, is reading data from the disc, the synchronous signal from the optical disc drive and the synchronous signal with respect to the information stored on the optical disc are compared for match. If the comparison result is that these two synchronous signals is matched, data stored on the optical disc then is decoded or read normally. In addition, the relation between the synchronous impulses is described as follows.
Referring to FIG. 2 that schematically illustrates a relation between the data synchronous impulses on the optical disc and predetermined synchronous impulses from the optical disc drive. As shown in FIG. 2, a predetermined synchronous impulse 202 (from the optical disc drive) and a data synchronous impulse 212 (from the disk) both have a width of t. Basically, when the predetermined synchronous impulse 202 and the data synchronous impulse 212 appear almost at the same time, these two synchronous impulses are considered as match. However, due to some limitation from the actual environment, there may be sometime a tiny difference between these two synchronous impulses. Thus, when considering this kind of issue about tiny difference, the optical disc drive will set a window 204 with length of w, where w>t, according to the predetermined synchronous impulse 202, so as to improve the tolerance during comparing the synchronous impulses. So, the data synchronous impulse 212 is compared with the window 204. When the data synchronous impulse 212 appears inside the window 204, it can be considered as a match between the predetermined synchronous impulse 202 and the data synchronous impulse 212.
However, in the case of a data gap on the optical disc recorded by BURN-Proof technology, even if the window is adjusted for increasing the tolerance of the error, it is still not able to make sure that the predetermined synchronous impulse for the optical disc drive always matches with the data synchronous impulse for the data on the optical disc. Referring to FIG. 3 that illustrates the waveform for the synchronous signal of the optical disc with the data gap. The data synchronous signal 310 with respect to the optical disc data includes the synchronous impulses 301, 303, 305, 307, 309 and 311. Since the data gap is located between the data synchronous impulse 305 and the data synchronous impulse 307, the abnormal distance between the data synchronous impulse 305 and the data synchronous impulse 307 will be greater than the normal distance (588 T) between the other data synchronous impulses. For example, the abnormal distance is 825 T. Then, the synchronous signal 350 for the optical disc drive includes the synchronous impulses 351, 353, 355, 357, 359, and 361. The optical disc drive will compare these synchronous impulses sequentially to check whether or not they match to the data synchronous impulses 301, 303, 305, 307, 309 and 311.
As shown in FIG. 3, only three predetermined synchronous impulses match with the data synchronous impulses. After the fourth synchronous impulse, all of the comparison results will not match. This is because the data synchronous impulse 307 is unexpectedly delayed after the data synchronous impulse 305 due to the data gap, but the optical disc drive cannot detect the occurrence of this situation. In this situation, the predetermined synchronous impulse 357 of the optical disc drive appears at the point of 588 T after the predetermined synchronous impulse 355. This will cause that the synchronous impulses are not matched for the first time. After the data synchronous impulse 307, the distance between the following data synchronous impulse on the optical disc becomes normal again, but the optical disc drive can only detect the data synchronous impulse on the optical disc within the window of the synchronous impulse. In other words, the optical disc drive cannot detect the delayed data synchronous impulses after the data synchronous impulse 307. Therefore, the optical disc drive still sets the predetermined synchronous impulses, so that the predetermined synchronous impulses 357 of the optical disc drive and other following predetermined synchronous impulses, such as the predetermined synchronous impulse 359, 361, and so on, will not be able to match with the data synchronous impulses.
Taking the current optical disc drive as an example, when the number of the synchronous impulses not matched is not over a certain limit number, such as 30, then even if the synchronous impulses cannot be matched, data still can be decoded by EDC (error detection code) and ECC (error correction code). However, according to the above descriptions, when the optical disc recorded by Burn-proof is read, the number of the synchronous impulses not matched may possibly be over the upper limit number, and therefore it causes the difficulty for the optical disc drive in decoding/reading data.